The present invention relates to electric motors and more particularly to an improved shaft mounted rotor core including permanent magnet segments mounted thereon and a method of manufacturing the same.
The rotors of speed control motors and of brushless DC electric motors include permanently magnetized bar segments which are held in firm relation to a rotor core by a suitable securing device. A number of past securing devices have included adhesives, clamps and wedges and, more recently, outer metallic sleeves, it being important that such devices be capable of withstanding the centrifugal forces created by the high speed of rotor rotation, as well as being capable of withstanding the axial and angular forces which can arise during manufacture, assembly and operation. Examples of rotor assemblies of the prior art include the circumferentially mounted laminated keeper, support ring and end plate arrangement of U.S. Pat. No. 3,221,194, issued to A. B. Blackburn on Nov. 30, 1965; the more recent wound, high modulus, composite fiber sleeve which is interference fit with a rotor hub assembly, as disclosed in U.S. Pat. No. 4,729,160, issued to G. W. Brown on Mar. 8, 1988; and the even more recent thin tubular metallic sleeve having residual tension to press the permanent magnets against the rotor core, as is disclosed in U.S. Pat. No. 4,742,259, issued to E. J. Schaefer et al. on May 3, 1988.
The present invention, recognizing that these past arrangements have been comparatively costly and difficult in both manufacture and assembly, as well as sometimes presenting problems of magnet chipping, of high electrical conductivity and of concomitant residual eddy currents, provides an improved, economical method of manufacturing and constructing a rotor assembly for an electric motor that minimizes and restrains stray magnetic chips which might occur during manufacture, assembly and operation, that closely controls the outer diameter of the rotor core/magnets assembly, that securely and compressively holds such rotor core/magnets assembly in fast relation, that is readily adaptable to various environmental conditions and configurations and that minimizes undesirable rotor eddy currents which might otherwise arise during rotor operations.
It is to be understood that various other features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth herein.